The present invention relates to a method and system for pulse interval modulation of wave energy and, in particular, to a method and system for encoding and decoding wave energy in accordance with selectable pulse interval modulation code sequences. The invention has particular utility in connection with laser designators and laser seekers and, while clearly not limited to this application, will be described hereinafter in connection with laser designators and seekers to facilitate an understanding thereof.
Laser target designators are used to covertly point out a target for laser seeker-equipped aircraft and for the laser designation of targets to provide semi-active guidance of free fall bombs or for the guidance of laser guided missiles. In such a system, pulses of laser energy of high peak power and short duration, e.g., a pulsed solid state laser such as Nd:YAC or Nd:Glass lasing material, are transmitted from the target designator to illuminate a target for tracking or guidance purposes. In an area containing numerous targets, several laser designators may be operating simultaneously and the return energy may cause interference between friendly systems. Thus it becomes necessary for each system operating in one area to be capable of distinguishing the signal from one designator from that of another designator.
In addition, with the proven effectiveness of laser designator systems it is likely that laser countermeasures will eventually be developed and become a serious threat to their continued success. It is thus of utmost importance that the system be relatively immune to at least those types of countermeasures such as PRF predicters and repeaters which could be presently available.
It is accordingly an object of the present invention to provide a novel coding method and system.
It is a more specific object of the present invention to provide a novel pulse interval modulation coding method and system particularly suited for use in connection with laser target designation systems.
It is yet another object of the present invention to provide a novel pulse interval modulation encoder for encoding the wave energy signal in accordance with a desired code sequence.
It is a further object of the present invention to provide a novel pulse interval modulation decoding method and system for selectively decoding pulse interval modulation encoded wave energy signals.
It is still another object of the present invention to provide a novel wave energy encoding and decoding method and system wherein a large number of different codes are provided.
It is still a further object of the present invention to provide a novel pulse interval modulation encoding and decoding system wherein the intervals between any two adjacent pairs of pulses is unique to a code sequence.
It is another object of the present invention to provide a novel method and system for selectively generating any of a large number of code sequences including selectable pulse repetition frequency (PRF) and pulse interval modulation (PIM) codes through a memory addressing technique.
It is yet a further object of the present invention to provide a novel method and coding system for pulse signals wherein a coded signal can be recognized as being the desired signal upon receipt of only three successive pulses of the signal.
It is still another object of the present invention to provide a novel method and system for encoding and decoding signals in accordance with a large number of selectable codes through a memory addressing technique wherein entirely new codes may be made available by merely changing an integrated circuit memory.
It is still a further object of the present invention to provide a novel method and system for decoding a pulse interval modulated signal wherein a signal from a repeater type countermeasure may be distinguished from a desired signal.
It is an additional object of the present invention to provide a novel method and laser target designation system wherein unique code sequences permit a laser seeker to operate selectively with a laser designator and provide a high degree of immunity to countermeasures.
It is yet another object of the present invention to provide a novel pulse interval modulation coding method and system utilizing novel pulse arrangements such that only one internal pair at any position in the code need be correctly identified in order that a particular code can be recognized.
These and other objects and advantages of the present invention will become apparent to one skilled in the art to which the invention pertains from a perusual of the following detailed description when read in conjunction with the attached drawings.